In recent years, low voltage differential signaling (LVDS) technology has been employed for speedup of signal transmission and reduction in power consumption. In a conventional LVDS interface employing this technology, signal transmission is made using differential amplitude obtained with constant current sources.
An LVDS interface as described above is applied to an interface between a controller LSI and a laser diode driver IC for a recordable DVD (digital versatile disc), for example. Specifically, the controller LSI generates a write waveform for the DVD, and the laser diode driver IC drives a semiconductor laser with a signal corresponding to the write waveform. The LVDS technology described above is used for this interface because the write waveform requires strict timing.
However, as the transmission rate becomes higher, for example, high-frequency loss increases on the transmission line, resulting in reduction in voltage amplitude at the receiver end. Therefore, in the cases of transmitting a random signal and the like, the amplitude may change depending on the pulse width, the eye opening may be narrowed, and pattern-dependent jitter tends to occur. In the application of the technology to DVDs as described above, a recording waveform can be transmitted without trouble as long as the recording speed is low. If high-speed recording is attempted, however, high-frequency loss on the transmission line will become too large to be negligible, and thus transmission of a correct write waveform will no more be possible.
To prevent the reduction in voltage amplitude at the receiver end as described above, a technology using a preemphasis circuit has been proposed, in which the amplitude of the output signal is increased at the time of state transition of an LVDS output circuit, to thereby suppress dulling of edge portions and thus reduce the amplitude change depending on the pulse width (See Patent Literature 1, for example).
Patent Literature 1: Japanese Laid-Open Patent Publication No. 2002-368600